Termination. A {@code Phaser} may enter a - * termination state in which all synchronization methods - * immediately return without updating phaser state or waiting for - * advance, and indicating (via a negative phase value) that execution - * is complete. Termination is triggered when an invocation of {@code - * onAdvance} returns {@code true}. As illustrated below, when - * phasers control actions with a fixed number of iterations, it is - * often convenient to override this method to cause termination when - * the current phase number reaches a threshold. Method {@link - * #forceTermination} is also available to abruptly release waiting - * threads and allow them to terminate. - * - *
Tiering. Phasers may be tiered (i.e., arranged - * in tree structures) to reduce contention. Phasers with large - * numbers of parties that would otherwise experience heavy + *
Termination. A phaser may enter a termination + * state in which all synchronization methods immediately return + * without updating phaser state or waiting for advance, and + * indicating (via a negative phase value) that execution is complete. + * Termination is triggered when an invocation of {@code onAdvance} + * returns {@code true}. The default implementation returns {@code + * true} if a deregistration has caused the number of registered + * parties to become zero. As illustrated below, when phasers control + * actions with a fixed number of iterations, it is often convenient + * to override this method to cause termination when the current phase + * number reaches a threshold. Method {@link #forceTermination} is + * also available to abruptly release waiting threads and allow them + * to terminate. + * + *
Tiering. Phasers may be tiered (i.e., + * constructed in tree structures) to reduce contention. Phasers with + * large numbers of parties that would otherwise experience heavy * synchronization contention costs may instead be set up so that * groups of sub-phasers share a common parent. This may greatly * increase throughput even though it incurs greater per-operation @@ -183,7 +185,7 @@ import java.util.concurrent.locks.LockSu * *
To create a set of tasks using a tree of phasers, * you could use code of the following form, assuming a - * Task class with a constructor accepting a phaser that + * Task class with a constructor accepting a {@code Phaser} that * it registers with upon construction: * *
{@code
@@ -203,8 +205,8 @@ import java.util.concurrent.locks.LockSu
* build(new Task[n], 0, n, new Phaser());}
*
* The best value of {@code TASKS_PER_PHASER} depends mainly on
- * expected barrier synchronization rates. A value as low as four may
- * be appropriate for extremely small per-barrier task bodies (thus
+ * expected synchronization rates. A value as low as four may
+ * be appropriate for extremely small per-phase task bodies (thus
* high rates), or up to hundreds for extremely large ones.
*
* Implementation notes: This implementation restricts the
@@ -224,8 +226,7 @@ public class Phaser {
*/
/**
- * Barrier state representation. Conceptually, a barrier contains
- * four values:
+ * Primary state representation, holding four fields:
*
* * unarrived -- the number of parties yet to hit barrier (bits 0-15)
* * parties -- the number of parties to wait (bits 16-31)
@@ -240,24 +241,24 @@ public class Phaser {
*/
private volatile long state;
- private static final int MAX_COUNT = 0xffff;
- private static final int MAX_PHASE = 0x7fffffff;
- private static final int PARTIES_SHIFT = 16;
- private static final int PHASE_SHIFT = 32;
- private static final long UNARRIVED_MASK = 0xffffL;
- private static final long PARTIES_MASK = 0xffff0000L;
- private static final long ONE_ARRIVAL = 1L;
- private static final long ONE_PARTY = 1L << PARTIES_SHIFT;
- private static final long TERMINATION_PHASE = -1L << PHASE_SHIFT;
+ private static final int MAX_PARTIES = 0xffff;
+ private static final int MAX_PHASE = 0x7fffffff;
+ private static final int PARTIES_SHIFT = 16;
+ private static final int PHASE_SHIFT = 32;
+ private static final int UNARRIVED_MASK = 0xffff; // to mask ints
+ private static final long PARTIES_MASK = 0xffff0000L; // to mask longs
+ private static final long ONE_ARRIVAL = 1L;
+ private static final long ONE_PARTY = 1L << PARTIES_SHIFT;
+ private static final long TERMINATION_BIT = 1L << 63;
// The following unpacking methods are usually manually inlined
private static int unarrivedOf(long s) {
- return (int) (s & UNARRIVED_MASK);
+ return (int)s & UNARRIVED_MASK;
}
private static int partiesOf(long s) {
- return ((int) (s & PARTIES_MASK)) >>> PARTIES_SHIFT;
+ return (int)s >>> PARTIES_SHIFT;
}
private static int phaseOf(long s) {
@@ -293,6 +294,22 @@ public class Phaser {
}
/**
+ * Returns message string for bounds exceptions on arrival.
+ */
+ private String badArrive(long s) {
+ return "Attempted arrival of unregistered party for " +
+ stateToString(s);
+ }
+
+ /**
+ * Returns message string for bounds exceptions on registration.
+ */
+ private String badRegister(long s) {
+ return "Attempt to register more than " +
+ MAX_PARTIES + " parties for " + stateToString(s);
+ }
+
+ /**
* Main implementation for methods arrive and arriveAndDeregister.
* Manually tuned to speed up and minimize race windows for the
* common case of just decrementing unarrived field.
@@ -302,119 +319,116 @@ public class Phaser {
* ONE_ARRIVAL|ONE_PARTY (for arriveAndDeregister)
*/
private int doArrive(long adj) {
- long s;
- int phase, unarrived;
- while ((phase = (int)((s = state) >>> PHASE_SHIFT)) >= 0) {
- if ((unarrived = (int)(s & UNARRIVED_MASK)) != 0) {
- if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s -= adj)) {
- if (unarrived == 1) {
- Phaser par;
- long p = s & PARTIES_MASK; // unshifted parties field
- long lu = p >>> PARTIES_SHIFT;
- int u = (int)lu;
- int nextPhase = (phase + 1) & MAX_PHASE;
- long next = ((long)nextPhase << PHASE_SHIFT) | p | lu;
- if ((par = parent) == null) {
- UNSAFE.compareAndSwapLong
- (this, stateOffset, s, onAdvance(phase, u)?
- next | TERMINATION_PHASE : next);
- releaseWaiters(phase);
- }
- else {
- par.doArrive(u == 0?
- ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL);
- if ((int)(par.state >>> PHASE_SHIFT) != nextPhase ||
- ((int)(state >>> PHASE_SHIFT) != nextPhase &&
- !UNSAFE.compareAndSwapLong(this, stateOffset,
- s, next)))
- reconcileState();
- }
+ for (;;) {
+ long s = state;
+ int unarrived = (int)s & UNARRIVED_MASK;
+ int phase = (int)(s >>> PHASE_SHIFT);
+ if (phase < 0)
+ return phase;
+ else if (unarrived == 0) {
+ if (reconcileState() == s) // recheck
+ throw new IllegalStateException(badArrive(s));
+ }
+ else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adj)) {
+ if (unarrived == 1) {
+ long p = s & PARTIES_MASK; // unshifted parties field
+ long lu = p >>> PARTIES_SHIFT;
+ int u = (int)lu;
+ int nextPhase = (phase + 1) & MAX_PHASE;
+ long next = ((long)nextPhase << PHASE_SHIFT) | p | lu;
+ final Phaser parent = this.parent;
+ if (parent == null) {
+ if (onAdvance(phase, u))
+ next |= TERMINATION_BIT;
+ UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
+ releaseWaiters(phase);
+ }
+ else {
+ parent.doArrive((u == 0) ?
+ ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL);
+ if ((int)(parent.state >>> PHASE_SHIFT) != nextPhase)
+ reconcileState();
+ else if (state == s)
+ UNSAFE.compareAndSwapLong(this, stateOffset, s,
+ next);
}
- break;
}
+ return phase;
}
- else if (state == s && reconcileState() == s) // recheck
- throw new IllegalStateException(badArrive());
}
- return phase;
- }
-
- /**
- * Returns message string for bounds exceptions on arrival.
- * Declared out of-line from doArrive to reduce string op bulk.
- */
- private String badArrive() {
- return ("Attempted arrival of unregistered party for " +
- this.toString());
}
/**
* Implementation of register, bulkRegister
*
- * @param registrations number to add to both parties and unarrived fields
+ * @param registrations number to add to both parties and
+ * unarrived fields. Must be greater than zero.
*/
private int doRegister(int registrations) {
- long adj = (long)registrations; // adjustment to state
- adj |= adj << PARTIES_SHIFT;
- Phaser par = parent;
- long s;
- int phase;
- while ((phase = (int)((s = (par == null? state : reconcileState()))
- >>> PHASE_SHIFT)) >= 0) {
- int parties = ((int)(s & PARTIES_MASK)) >>> PARTIES_SHIFT;
- if (parties != 0 && (s & UNARRIVED_MASK) == 0)
- internalAwaitAdvance(phase, null); // wait for onAdvance
- else if (parties + registrations > MAX_COUNT)
- throw new IllegalStateException(badRegister());
- else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s + adj))
- break;
+ // adjustment to state
+ long adj = ((long)registrations << PARTIES_SHIFT) | registrations;
+ final Phaser parent = this.parent;
+ for (;;) {
+ long s = (parent == null) ? state : reconcileState();
+ int parties = (int)s >>> PARTIES_SHIFT;
+ int phase = (int)(s >>> PHASE_SHIFT);
+ if (phase < 0)
+ return phase;
+ else if (registrations > MAX_PARTIES - parties)
+ throw new IllegalStateException(badRegister(s));
+ else if ((parties == 0 && parent == null) || // first reg of root
+ ((int)s & UNARRIVED_MASK) != 0) { // not advancing
+ if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s + adj))
+ return phase;
+ }
+ else if (parties != 0) // wait for onAdvance
+ root.internalAwaitAdvance(phase, null);
+ else { // 1st registration of child
+ synchronized (this) { // register parent first
+ if (reconcileState() == s) { // recheck under lock
+ parent.doRegister(1); // OK if throws IllegalState
+ for (;;) { // simpler form of outer loop
+ s = reconcileState();
+ phase = (int)(s >>> PHASE_SHIFT);
+ if (phase < 0 ||
+ UNSAFE.compareAndSwapLong(this, stateOffset,
+ s, s + adj))
+ return phase;
+ }
+ }
+ }
+ }
}
- return phase;
}
/**
- * Returns message string for bounds exceptions on registration
- */
- private String badRegister() {
- return ("Attempt to register more than " + MAX_COUNT + " parties for "+
- this.toString());
- }
-
- /**
- * Recursively resolves lagged phase propagation from root if
- * necessary.
+ * Recursively resolves lagged phase propagation from root if necessary.
*/
private long reconcileState() {
Phaser par = parent;
- if (par == null)
- return state;
- Phaser rt = root;
- long s;
- int phase, rPhase;
- while ((phase = (int)((s = state) >>> PHASE_SHIFT)) >= 0 &&
- (rPhase = (int)(rt.state >>> PHASE_SHIFT)) != phase) {
- if (rPhase < 0 || (s & UNARRIVED_MASK) == 0) {
- long ps = par.parent == null? par.state : par.reconcileState();
- int pPhase = (int)(ps >>> PHASE_SHIFT);
- if (pPhase < 0 || pPhase == ((phase + 1) & MAX_PHASE)) {
- if (state != s)
- continue;
- long p = s & PARTIES_MASK;
- long next = ((((long) pPhase) << PHASE_SHIFT) |
- (p >>> PARTIES_SHIFT) | p);
- if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next))
- return next;
+ long s = state;
+ if (par != null) {
+ Phaser rt = root;
+ int phase, rPhase;
+ while ((phase = (int)(s >>> PHASE_SHIFT)) >= 0 &&
+ (rPhase = (int)(rt.state >>> PHASE_SHIFT)) != phase) {
+ if (par != rt && (int)(par.state >>> PHASE_SHIFT) != rPhase)
+ par.reconcileState();
+ else if (rPhase < 0 || ((int)s & UNARRIVED_MASK) == 0) {
+ long u = s & PARTIES_MASK; // reset unarrived to parties
+ long next = ((((long) rPhase) << PHASE_SHIFT) | u |
+ (u >>> PARTIES_SHIFT));
+ UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
}
+ s = state;
}
- if (state == s)
- releaseWaiters(phase); // help release others
}
return s;
}
/**
- * Creates a new phaser without any initially registered parties,
- * initial phase number 0, and no parent. Any thread using this
+ * Creates a new phaser with no initially registered parties, no
+ * parent, and initial phase number 0. Any thread using this
* phaser will need to first register for it.
*/
public Phaser() {
@@ -423,9 +437,10 @@ public class Phaser {
/**
* Creates a new phaser with the given number of registered
- * unarrived parties, initial phase number 0, and no parent.
+ * unarrived parties, no parent, and initial phase number 0.
*
- * @param parties the number of parties required to trip barrier
+ * @param parties the number of parties required to advance to the
+ * next phase
* @throws IllegalArgumentException if parties less than zero
* or greater than the maximum number of parties supported
*/
@@ -434,10 +449,7 @@ public class Phaser {
}
/**
- * Creates a new phaser with the given parent, without any
- * initially registered parties. If parent is non-null this phaser
- * is registered with the parent and its initial phase number is
- * the same as that of parent phaser.
+ * Equivalent to {@link #Phaser(Phaser, int) Phaser(parent, 0)}.
*
* @param parent the parent phaser
*/
@@ -447,41 +459,49 @@ public class Phaser {
/**
* Creates a new phaser with the given parent and number of
- * registered unarrived parties. If parent is non-null, this phaser
- * is registered with the parent and its initial phase number is
- * the same as that of parent phaser.
+ * registered unarrived parties. Registration and deregistration
+ * of this child phaser with its parent are managed automatically.
+ * If the given parent is non-null, whenever this child phaser has
+ * any registered parties (as established in this constructor,
+ * {@link #register}, or {@link #bulkRegister}), this child phaser
+ * is registered with its parent. Whenever the number of
+ * registered parties becomes zero as the result of an invocation
+ * of {@link #arriveAndDeregister}, this child phaser is
+ * deregistered from its parent.
*
* @param parent the parent phaser
- * @param parties the number of parties required to trip barrier
+ * @param parties the number of parties required to advance to the
+ * next phase
* @throws IllegalArgumentException if parties less than zero
* or greater than the maximum number of parties supported
*/
public Phaser(Phaser parent, int parties) {
- if (parties < 0 || parties > MAX_COUNT)
+ if (parties >>> PARTIES_SHIFT != 0)
throw new IllegalArgumentException("Illegal number of parties");
- int phase;
+ long s = ((long) parties) | (((long) parties) << PARTIES_SHIFT);
this.parent = parent;
if (parent != null) {
Phaser r = parent.root;
this.root = r;
this.evenQ = r.evenQ;
this.oddQ = r.oddQ;
- phase = parent.register();
+ if (parties != 0)
+ s |= ((long)(parent.doRegister(1))) << PHASE_SHIFT;
}
else {
this.root = this;
this.evenQ = new AtomicReference It is a usage error for an unregistered party to invoke this
+ * method. However, this error may result in an {@code
+ * IllegalStateException} only upon some subsequent operation on
+ * this phaser, if ever.
*
* @return the arrival phase number, or a negative value if terminated
* @throws IllegalStateException if not terminated and the number
@@ -527,13 +551,16 @@ public class Phaser {
}
/**
- * Arrives at the barrier and deregisters from it without waiting
- * for others. Deregistration reduces the number of parties
- * required to trip the barrier in future phases. If this phaser
+ * Arrives at this phaser and deregisters from it without waiting
+ * for others to arrive. Deregistration reduces the number of
+ * parties required to advance in future phases. If this phaser
* has a parent, and deregistration causes this phaser to have
- * zero parties, this phaser also arrives at and is deregistered
- * from its parent. It is an unenforced usage error for an
- * unregistered party to invoke this method.
+ * zero parties, this phaser is also deregistered from its parent.
+ *
+ * It is a usage error for an unregistered party to invoke this
+ * method. However, this error may result in an {@code
+ * IllegalStateException} only upon some subsequent operation on
+ * this phaser, if ever.
*
* @return the arrival phase number, or a negative value if terminated
* @throws IllegalStateException if not terminated and the number
@@ -544,83 +571,88 @@ public class Phaser {
}
/**
- * Arrives at the barrier and awaits others. Equivalent in effect
+ * Arrives at this phaser and awaits others. Equivalent in effect
* to {@code awaitAdvance(arrive())}. If you need to await with
* interruption or timeout, you can arrange this with an analogous
* construction using one of the other forms of the {@code
* awaitAdvance} method. If instead you need to deregister upon
- * arrival, use {@link #arriveAndDeregister}. It is an unenforced
- * usage error for an unregistered party to invoke this method.
+ * arrival, use {@code awaitAdvance(arriveAndDeregister())}.
+ *
+ * It is a usage error for an unregistered party to invoke this
+ * method. However, this error may result in an {@code
+ * IllegalStateException} only upon some subsequent operation on
+ * this phaser, if ever.
*
* @return the arrival phase number, or a negative number if terminated
* @throws IllegalStateException if not terminated and the number
* of unarrived parties would become negative
*/
public int arriveAndAwaitAdvance() {
- return awaitAdvance(arrive());
+ return awaitAdvance(doArrive(ONE_ARRIVAL));
}
/**
- * Awaits the phase of the barrier to advance from the given phase
- * value, returning immediately if the current phase of the
- * barrier is not equal to the given phase value or this barrier
- * is terminated.
+ * Awaits the phase of this phaser to advance from the given phase
+ * value, returning immediately if the current phase is not equal
+ * to the given phase value or this phaser is terminated.
*
* @param phase an arrival phase number, or negative value if
* terminated; this argument is normally the value returned by a
- * previous call to {@code arrive} or its variants
+ * previous call to {@code arrive} or {@code arriveAndDeregister}.
* @return the next arrival phase number, or a negative value
* if terminated or argument is negative
*/
public int awaitAdvance(int phase) {
+ Phaser rt;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- int p = (int)((parent==null? state : reconcileState()) >>> PHASE_SHIFT);
- if (p != phase)
- return p;
- return internalAwaitAdvance(phase, null);
+ if (p == phase &&
+ (p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase)
+ return rt.internalAwaitAdvance(phase, null);
+ return p;
}
/**
- * Awaits the phase of the barrier to advance from the given phase
+ * Awaits the phase of this phaser to advance from the given phase
* value, throwing {@code InterruptedException} if interrupted
- * while waiting, or returning immediately if the current phase of
- * the barrier is not equal to the given phase value or this
- * barrier is terminated.
+ * while waiting, or returning immediately if the current phase is
+ * not equal to the given phase value or this phaser is
+ * terminated.
*
* @param phase an arrival phase number, or negative value if
* terminated; this argument is normally the value returned by a
- * previous call to {@code arrive} or its variants
+ * previous call to {@code arrive} or {@code arriveAndDeregister}.
* @return the next arrival phase number, or a negative value
* if terminated or argument is negative
* @throws InterruptedException if thread interrupted while waiting
*/
public int awaitAdvanceInterruptibly(int phase)
throws InterruptedException {
+ Phaser rt;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- int p = (int)((parent==null? state : reconcileState()) >>> PHASE_SHIFT);
- if (p != phase)
- return p;
- QNode node = new QNode(this, phase, true, false, 0L);
- p = internalAwaitAdvance(phase, node);
- if (node.wasInterrupted)
- throw new InterruptedException();
- else
- return p;
+ if (p == phase &&
+ (p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase) {
+ QNode node = new QNode(this, phase, true, false, 0L);
+ p = rt.internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
+ }
+ return p;
}
/**
- * Awaits the phase of the barrier to advance from the given phase
+ * Awaits the phase of this phaser to advance from the given phase
* value or the given timeout to elapse, throwing {@code
* InterruptedException} if interrupted while waiting, or
- * returning immediately if the current phase of the barrier is
- * not equal to the given phase value or this barrier is
- * terminated.
+ * returning immediately if the current phase is not equal to the
+ * given phase value or this phaser is terminated.
*
* @param phase an arrival phase number, or negative value if
* terminated; this argument is normally the value returned by a
- * previous call to {@code arrive} or its variants
+ * previous call to {@code arrive} or {@code arriveAndDeregister}.
* @param timeout how long to wait before giving up, in units of
* {@code unit}
* @param unit a {@code TimeUnit} determining how to interpret the
@@ -634,76 +666,90 @@ public class Phaser {
long timeout, TimeUnit unit)
throws InterruptedException, TimeoutException {
long nanos = unit.toNanos(timeout);
+ Phaser rt;
+ int p = (int)(state >>> PHASE_SHIFT);
if (phase < 0)
return phase;
- int p = (int)((parent==null? state : reconcileState()) >>> PHASE_SHIFT);
- if (p != phase)
- return p;
- QNode node = new QNode(this, phase, true, true, nanos);
- p = internalAwaitAdvance(phase, node);
- if (node.wasInterrupted)
- throw new InterruptedException();
- else if (p == phase)
- throw new TimeoutException();
- else
- return p;
+ if (p == phase &&
+ (p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase) {
+ QNode node = new QNode(this, phase, true, true, nanos);
+ p = rt.internalAwaitAdvance(phase, node);
+ if (node.wasInterrupted)
+ throw new InterruptedException();
+ else if (p == phase)
+ throw new TimeoutException();
+ }
+ return p;
}
/**
- * Forces this barrier to enter termination state. Counts of
- * arrived and registered parties are unaffected. If this phaser
- * has a parent, it too is terminated. This method may be useful
- * for coordinating recovery after one or more tasks encounter
- * unexpected exceptions.
+ * Forces this phaser to enter termination state. Counts of
+ * arrived and registered parties are unaffected. If this phaser
+ * is a member of a tiered set of phasers, then all of the phasers
+ * in the set are terminated. If this phaser is already
+ * terminated, this method has no effect. This method may be
+ * useful for coordinating recovery after one or more tasks
+ * encounter unexpected exceptions.
*/
public void forceTermination() {
- Phaser r = root; // force at root then reconcile
+ // Only need to change root state
+ final Phaser root = this.root;
long s;
- while ((s = r.state) >= 0)
- UNSAFE.compareAndSwapLong(r, stateOffset, s, s | TERMINATION_PHASE);
- reconcileState();
- releaseWaiters(0); // signal all threads
- releaseWaiters(1);
+ while ((s = root.state) >= 0) {
+ if (UNSAFE.compareAndSwapLong(root, stateOffset,
+ s, s | TERMINATION_BIT)) {
+ releaseWaiters(0); // signal all threads
+ releaseWaiters(1);
+ return;
+ }
+ }
}
/**
* Returns the current phase number. The maximum phase number is
* {@code Integer.MAX_VALUE}, after which it restarts at
- * zero. Upon termination, the phase number is negative.
+ * zero. Upon termination, the phase number is negative,
+ * in which case the prevailing phase prior to termination
+ * may be obtained via {@code getPhase() + Integer.MIN_VALUE}.
*
* @return the phase number, or a negative value if terminated
*/
public final int getPhase() {
- return (int)((parent == null? state : reconcileState()) >>> PHASE_SHIFT);
+ return (int)(root.state >>> PHASE_SHIFT);
}
/**
- * Returns the number of parties registered at this barrier.
+ * Returns the number of parties registered at this phaser.
*
* @return the number of parties
*/
public int getRegisteredParties() {
- return partiesOf(parent == null? state : reconcileState());
+ return partiesOf(state);
}
/**
* Returns the number of registered parties that have arrived at
- * the current phase of this barrier.
+ * the current phase of this phaser.
*
* @return the number of arrived parties
*/
public int getArrivedParties() {
- return arrivedOf(parent == null? state : reconcileState());
+ long s = state;
+ int u = unarrivedOf(s); // only reconcile if possibly needed
+ return (u != 0 || parent == null) ?
+ partiesOf(s) - u :
+ arrivedOf(reconcileState());
}
/**
* Returns the number of registered parties that have not yet
- * arrived at the current phase of this barrier.
+ * arrived at the current phase of this phaser.
*
* @return the number of unarrived parties
*/
public int getUnarrivedParties() {
- return unarrivedOf(parent == null? state : reconcileState());
+ int u = unarrivedOf(state);
+ return (u != 0 || parent == null) ? u : unarrivedOf(reconcileState());
}
/**
@@ -726,47 +772,56 @@ public class Phaser {
}
/**
- * Returns {@code true} if this barrier has been terminated.
+ * Returns {@code true} if this phaser has been terminated.
*
- * @return {@code true} if this barrier has been terminated
+ * @return {@code true} if this phaser has been terminated
*/
public boolean isTerminated() {
- return (parent == null? state : reconcileState()) < 0;
+ return root.state < 0L;
}
/**
* Overridable method to perform an action upon impending phase
* advance, and to control termination. This method is invoked
- * upon arrival of the party tripping the barrier (when all other
+ * upon arrival of the party advancing this phaser (when all other
* waiting parties are dormant). If this method returns {@code
- * true}, then, rather than advance the phase number, this barrier
+ * true}, then, rather than advance the phase number, this phaser
* will be set to a final termination state, and subsequent calls
* to {@link #isTerminated} will return true. Any (unchecked)
* Exception or Error thrown by an invocation of this method is
- * propagated to the party attempting to trip the barrier, in
+ * propagated to the party attempting to advance this phaser, in
* which case no advance occurs.
*
* The arguments to this method provide the state of the phaser
* prevailing for the current transition. The effects of invoking
- * arrival, registration, and waiting methods on this Phaser from
+ * arrival, registration, and waiting methods on this phaser from
* within {@code onAdvance} are unspecified and should not be
* relied on.
*
- * If this Phaser is a member of a tiered set of Phasers, then
- * {@code onAdvance} is invoked only for its root Phaser on each
+ * If this phaser is a member of a tiered set of phasers, then
+ * {@code onAdvance} is invoked only for its root phaser on each
* advance.
*
- * The default version returns {@code true} when the number of
- * registered parties is zero. Normally, overrides that arrange
- * termination for other reasons should also preserve this
- * property.
+ * To support the most common use cases, the default
+ * implementation of this method returns {@code true} when the
+ * number of registered parties has become zero as the result of a
+ * party invoking {@code arriveAndDeregister}. You can disable
+ * this behavior, thus enabling continuation upon future
+ * registrations, by overriding this method to always return
+ * {@code false}:
+ *
+ * {@code
+ * Phaser phaser = new Phaser() {
+ * protected boolean onAdvance(int phase, int parties) { return false; }
+ * }}
*
- * @param phase the phase number on entering the barrier
+ * @param phase the current phase number on entry to this method,
+ * before this phaser is advanced
* @param registeredParties the current number of registered parties
- * @return {@code true} if this barrier should terminate
+ * @return {@code true} if this phaser should terminate
*/
protected boolean onAdvance(int phase, int registeredParties) {
- return registeredParties <= 0;
+ return registeredParties == 0;
}
/**
@@ -776,45 +831,43 @@ public class Phaser {
* followed by the number of registered parties, and {@code
* "arrived = "} followed by the number of arrived parties.
*
- * @return a string identifying this barrier, as well as its state
+ * @return a string identifying this phaser, as well as its state
*/
public String toString() {
- long s = reconcileState();
+ return stateToString(reconcileState());
+ }
+
+ /**
+ * Implementation of toString and string-based error messages
+ */
+ private String stateToString(long s) {
return super.toString() +
"[phase = " + phaseOf(s) +
" parties = " + partiesOf(s) +
" arrived = " + arrivedOf(s) + "]";
}
+ // Waiting mechanics
+
/**
- * Removes and signals threads from queue for phase
+ * Removes and signals threads from queue for phase.
*/
private void releaseWaiters(int phase) {
- AtomicReference